The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Many runners desire to monitor speed or pace in order to assess performance, determine whether personal goals are being met and, ultimately, improve running performance. To this end, many runners carry smartphones and/or smart watches that include Global Navigation Satellite System (GNSS) receivers. GNSS may include one or more of the Global Positioning System (GPS) of the United States of America, GLONASS of Russia, BeiDou of China, Galileo of Europe, QZSS of Japan, and/or IRNSS of India. Speed estimates are derived from GNSS locations, or from the Doppler shifts of GNSS signals. Unfortunately, GNSS-based speed measurements tend to be noisy and therefore inaccurate. Noise/inaccuracy is caused by factors such as blockage of GNSS signals (e.g., when running inside a building or under a bridge), multipath reflection of GNSS signals (e.g., when running in a downtown area of a city), and arm swing (e.g., if the device is handheld or worn on the wrist or upper arm). These factors can easily cause an instantaneous, GNSS-based speed measurement to be up to 50% lower than, or 100% higher than, the user's true speed at any given moment. To reduce the level of noise, some devices apply heavy smoothing/averaging to the GNSS speed measurements. While this may reduce the magnitude of speed measurement errors when the user's pace is fairly constant, the technique is insufficiently responsive to large and sudden changes in speed, such as when a user runs intervals, or briefly stops at a crosswalk, etc.